package algorithm.problems.backtracking;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Created by gouthamvidyapradhan on 12/04/2017.
 * Given a collection of numbers that might contain duplicates, return all possible unique permutations.
 * <p>
 * For example,
 * [1,1,2] have the following unique permutations:
 * [
 * [1,1,2],
 * [1,2,1],
 * [2,1,1]
 * ]
 */
public class PermutationsII {
    public static void main(String[] args) {
        int[] A = {1, 2, 2};
        System.out.println(new PermutationsII().permuteUnique(A));
    }

    public List<List<Integer>> permuteUnique(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        Arrays.sort(nums);
        nextPermutation(0, nums, result);
        return result;
    }

    private void nextPermutation(int i, int[] nums, List<List<Integer>> result) {
        if (i == nums.length - 1) {
            List<Integer> list = new ArrayList<>();
            for (int n : nums)
                list.add(n);
            result.add(list);
        } else {
            for (int j = i, l = nums.length; j < l; j++) {
                if (j > i && nums[j] == nums[i]) continue;
                swap(nums, i, j);
                nextPermutation(i + 1, Arrays.copyOf(nums, nums.length), result);
            }
        }
    }

    private void swap(int[] a, int i, int j) {
        int tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    }
}
